1. Field of the Invention
The present invention relates to an imaging lens system, and more particularly, to an optical system used in a compact imaging module.
2. Description of the Prior Art
In recent years, with the popularity of imaging modules, the demand for compact photographing lens assemblies is increasing, and the sensor of a general photographing lens assembly is none other than CCD (charge coupled device) or CMOS (Complementary Metal Oxide Semiconductor). Furthermore, as advanced semiconductor manufacturing technology has allowed the pixel size of sensors to be reduced and electronic products have become more compact and powerful, there is an increasing demand for compact imaging lens assemblies featuring better image quality.
In order to correct aberrations, a conventional imaging lens system, such as the optical lens system for taking image disclosed in U.S. Pat. No. 7,529,041, generally adopts the so-called triplet design and comprises, in order from the object side to the image side: a first lens element with positive refractive power; a second lens element with negative refractive power; and a third lens element with positive refractive power. Both surfaces of the first lens element are convex and this enables an effective reduction of the total track length of the system. However, such an arrangement may render the refractive power of the first lens element excessive and cause the system to generate more aberrations that affect the image quality. Moreover, the proportions of the refractive power contributed by the second and third lens elements have to be increased to balance the refractive power of the first lens element. Consequently, the sensitivity of the system will be increased, making it more difficult to control the manufacturing yields of the imaging lens system.